The present invention is directed generally to cleaning a surface and, more particularly, to cleaning the surface of a semiconductor substrate following a chemical, mechanical, or chemical mechanical polishing of the substrate surface.
Integrated circuits are typically constructed by depositing layers of various materials to form circuit components on a wafer shaped semiconductor substrate. The formation of the circuit components in each layer generally produces a rough, or nonplanar, topography on the surface of the wafer. A rough surface on an underlying layer increases the likelihood of a defect occurring in subsequently deposited layers that can result in flawed or improperly performing circuitry. Thus, the efficient production of integrated circuits depends, in part, on the ability to produce smooth, or planarized, surfaces on which subsequent circuitry can be precisely deposited.
A smooth surface on the layers is generally provided by performing a planarization process. There are numerous processes used to planarize a surface, which are generally classified in the art as chemical planarization (such as etching), mechanical planarizing, and/or chemical-mechanical planarizing.
While each of the planarization processes generally provides for a more smooth surface, residual chemicals and/or particles may remain on the surface following the process. The residual chemicals and particles also must be removed to prevent defect formation in subsequent layers. Such defects may result either physically from the presence of particles or chemically via the interaction of the residual chemicals or particles with the composition of the subsequently deposited layer.
Post-planarization cleaning of the surface is often performed using various methods depending upon the composition of the layer and any residual chemicals and particles that may be present on the layer. The cleaning methods are generally wet cleaning procedures that include chemical cleaning, mechanical scrubbing and other surface agitation techniques.
For example, some cleaning methods are purely chemical or mechanical, such as those described in U.S. Pat. No. 5,181,985 and Japanese Patent Abstract Publication No. 02-281,733, respectively. As might be expected, these methods are generally more suitable for the removal of either residual chemicals or particles, respectively. Other methods, such as those described in U.S. Pat. Nos. 5,475,889, 5,442,828, 5,529,638, and 5,555,177 employ mechanical brush scrubbers that are used to brush particles from the surface, while liquid jet sprays are used to wet the surface, and possibly dislodge particles, with deionized water and/or cleaning solutions. While many of these methods provide both chemical and mechanical cleaning of the surfaces, the cleaning results derived from the methods are subject to variation due to uneven chemical distribution on the surface of the substrate which contributes to varying mechanical cleaning effectiveness and the potential for uneven drying of the surface subsequent to cleaning.
Still other methods rely on other forms of agitation to remove the residual chemicals or particles. For example, U.S. Pat. No. 5,451,267 discloses an apparatus in which a cleaning solution is agitated by bubbling a gas through the cleaning vessel to produce liquid flow past the surface to be cleaned. U.S. Pat. Nos. 3,893,869, 4,804,007, 4,869,278, 4,998,549, 5,037,481, 5,365,960, 5,368,054, 5,427,622, 5,533,540, and 5,534,076 disclose cleaning systems in which cleaning solutions and surfaces are acoustically agitated. The efficiency of these agitation methods depends upon the effectiveness of the flowing liquid or the acoustic energy at dislodging particles from the surface. It is expected that the effectiveness of the methods will depend upon the composition of the particle and the layer, as well as the particle sizes and surface affinity. It is therefore difficult to provide an effective cleaning procedure given the expected variations in residual chemicals and particle distributions during production processing of semiconductor substrates.
Following wet cleaning procedures, as the fluid on the surface of the substrate evaporates, particles and other contaminants contained in the residual cleaning fluid may settle on the surface to form water marks. Therefore, it is desirable to dry the surface following a wet cleaning procedure in a manner that minimizes evaporation and the resulting formation of water marks. A number of methods, such as those described in U.S. Pat. Nos. 5,660,642, 5,569,330, 5,653,045, 5,634,978, 5,601,655, and 5,571,337, utilize the formation of a Marangoni flow to decrease the surface tension of fluid on the surface, thereby facilitating the removal of the water from the surface prior to evaporation.
As is evident from the aforementioned discussion, a number of difficulties remain with present cleaning methods that need to be overcome to provide an effective cleaning method for surfaces. The present invention serves to provide methods and apparatuses for cleaning surfaces, in particular, the surfaces of semiconductor substrate layers.